Polyisobutylene nucleating agents for expandable styrene polymer compositions

ABSTRACT

Disclosed are a composition and process for the preparation of expandable styrene polymers wherein low molecular weight isobutylene polymers are employed in an amount of from about 0.02 to about 0.15% by weight based upon the styrene polymer as a nucleating agent to produce an expanded styrene polymer having a very small average cell size.

United States Patent [1 1 Stevenson [451 Dec. 30, 1975 [54] POLYISOBUTYLENE NUCLEATING AGENTS FOR EXPANDABLE STYRENE POLYMER COMPOSITIONS [75] Inventor: John L. Stevenson, Big Spring, Tex.

[73] Assignee: Cosden Oil & Chemical Company,

Big Spring, Tex.

[22] Filed: Aug. 31, 1973 [2]] Appl. No.: 393,454

[52] US. Cl. 260/2.5 B; 260/25 E; 260/25 HA; 260/2.5 HB [51] Int. Cl. C03J 9/00 [58] Field of Search 260/2.5 E, 2.5 B, 25 HA, 260/25 HB [56] References Cited UNITED STATES PATENTS 2,857,339 10/1958 Colwell "260/258 2,962,456 11/1960 Carlson, Jr 260/25 B 3,072,584 1/1963 Korpovich 3,407,151 10/1968 Overcashier et a1. 260/25 E Primary Examiner-Richard B. Turer [57] ABSTRACT a very small average cell size.

14 Claims, No Drawings POLYISOBUTYLENE NUCLEATING AGENTS FOR EXPANDABLE STYRENE POLYMER COMPOSITIONS BACKGROUND OF THE INVENTION The present invention relates to the production of expandable styrene polymers and more especially to the use of low molecular weight isobutylene polymers as nucleating agents for expandable styrene polymer compositions.

It is known in accordance with the prior art to utilize various nucleating agents in the preparation of expandable styrene polymer compositions. Some of the more well known nucleating agents include, for example,

finely divided inorganic solid fillers, like silicon dioxide, calcium silicate, magnesium silicate and diatomaceous earth, inorganic carbonates with organic acids,

ammonium salts of carboxylic acids, inorganic ammonium salts, hydrated inorganic salts, metal stearates,

certain pigments, orthoboric acid and various combinations thereof. These conventional nucleating agents are typically incorporated into the styrene polymer compositions at the time polymerization of the monomeric styrene is carried out or by blending with a preformed polymer.

The success of a nucleating agent is measured by its ability to lower the average cell size of the styrene polymer composition upon expansion thereof. The

various prior art nucleating agents mentioned hereinabove exhibit varying degrees of effectiveness in this regard, but some are relatively expensive and with others there are experienced certain difficulties in incorporating same into the styrene polymer compositions or the properties and/or appearance of the polymer is affected by such incorporation. Therefore, there exists today in the art a definite need for a nucleating agent suitable for the production of expandable styrene polymer compositions which is effective in reducing the average cell size of the expanded polymer composi- SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a nucleating agent for the production of expandable styrene polymer compositions which is very effective in reducing the average cell size of the expanded polymer compositions when employed in very small amounts.

It is another object of the present invention to provide a nucleating agent for the production of expandable styrene polymer compositions which is readily obtainable and is inexpensive and which is in all respects compatible with the subject polymer compositions.

Another object of the present invention resides in the provision of an improved composition suitable for the preparation of expanded styrene polymers.

It is yet another object of the invention to provide a process for the production of foamed styrene polymer compositions.

In accomplishing the foregoing objects, there has been provided in accordance with the present invention a composition and process for the production of expanded styrene polymercompositions. This process 0 most preferably between about 0.05 and 0.1%. Similarly, it is preferred that the molecular weight of the isobutylene polymer is between about 1,000 and 3,000,

V whereas in the most preferred embodiment the molecular weight ranges between about 1,350 and 2,700.

Other objects, features and advantages of the present invention will become apparent to a person skilled in the art from the detailed description of the invention which follows.

DETAILED DESCRIPTION OF THE INVENTION It has been discovered in accordance with the present invention that low molecular weight isobutylene polymers may advantageously be employed as nucleating agents in the production of expandable styrene polymer compositions. The isobutylene polymers are particularly effective in reducing the average cell size of the styrene polymer compositions upon expansion. This utility and advantageous result are believed to be particularly surprising in view of the fact that the subject isobutylene polymers are so significantly different from any nucleating agents which have heretofore been employed in the production of expandable styrene polymer products.

The isobutylene polymers according to the present invention are preferably homopolymers of isobutylene but include also C C lower olefin hydrocarbons containing at least about isobutylene monomer units and typically including minor amounts of normal-butylene monomer units and relatively small amounts of other lower olefins. The isobutylene polymers employed in the present invention are those having a molecular weight (number average) of between about 500 and 5,000, although it is preferred that the molecular weight thereof range between about 1,000 and 3,000. In the most preferred embodiment of the invention, the isobutylene polymer has a molecular weight between about 1,350 and 2,700. The polymers are characterized as long chain hydrophobic molecules with methyl side group chains, and the polymeric materials are pale colored and relatively inert chemically. The polymers are typically quite viscous, but the viscosity varies considerably in accordance with the molecular weight of the polymers. Also, the polymers advantageously show no toxicity whatsoever as regards humans and animals. This represents an important factor since expanded polystyrene compositions are widely utilized for the manufacture of drinking cups, meat trays, and other molded products which come directly into contact with food and beverages.

The isobutylene polymers employed in accordance with the present invention can be prepared by means of known procedures, and suitable products are available commercially. In a typical method for the preparation of the subject isobutylene polymers, a hydrocarbon feed consisting essentially of isobutylene monomer is contacted with a Friedel-Crafts catalyst at a temperature above about 45F., whereupon a suitable low molecular weight polymer is produced. See, for example, the disclosure of U.S. Pat. No. 2,957,930. Polymers falling within the upper portion of the molecular weight range specified hereinabove may be produced by further contacting the foregoing low molecular weight polyisobutylene with about 1 to of a Friedel-Crafts catalyst for periods of about minutes to 2 hours and at a temperature of from about 10 to 200F. See, for example, U.S. Pat. No. 3,375,295. Other suitable procedures for the preparation of low molecular weight isobutylene polymers are described in U.S. Pat. Nos. 3,501,551, 3,073,876, 3,242,158, and 3,356,661. The most preferred isobutylene polymers are those available from Cosden Oil & Chemical Company under the trademark POLYVIS. 4

In order to accomplish the desired degree of diminution in average cell size of the expanded styrene polymer compositions, there is incorporated therein from about 0.02 to 0.15% by weight based upon the styrene polymer of the subject isobutylene polymer nucleating agent. It is preferred that the amount of isobutylene polymer added falls within the range ofabout 0.03 to 0.12% by weight, and most preferably, the amount of isobutylene polymer ranges between about 0.05 and 0.1% by weight based on the styrene polymer.

Incorporation of the isobutylene polymer nucleating agent into the styrene polymer compositions intended for expansion is accomplished typically by incorporating the desired amount of nucleating agent into the polymerization system wherein the styrene polymers are produced. This may be accomplished simply by adding the desired amount of nucleating agent into any of the conventional polymerization systems employed for the production of styrene polymer compositions, e.g., suspension polymerization, bulk polymerization and combinations thereof. When the addition of nucleating agent is carried out in this manner, the nucleating agent may be added at any point in time prior to polymerization being 75% complete. It is also possible to incorporate the isobutylene polymer nucleating agent into the styrene polymer at a point in time subsequent to polymerization of the styrene monomer, as for example, by physical blending of the nucleating agent and the styrene polymer on a Banbury mixer or the like. However, it is to be understood that the most preferred embodiment of the present invention involves the production of expandable polystyrene beads by suspension polymerization techniques. Therefore, the most preferred and most valuable application of the subject invention concerns the incorporation of the isobutylene polymer nucleating agent directly into a styrene suspension polymerization system before or during the polymerization reaction such that there are produced styrene polymer beads having the nucleating agent already incorporated therein. The styrene polymer beads also have incorporated thereinto a suitable blowing agent, preferably a latent, heat activatable blowing agent, and thus, may be subsequently expanded as desired.

The present invention is applicable to the well-defined class of polymeric materials known as styrene polymers. The term styrene polymer as employed herein is to be understood as including homopolystyrene, copolymers of styrene with minor amounts of other ethylenically unsaturated monomers copolymerizable therewith and also homopolymers and copolymers derived from substituted styrene monomers, such as lower alkyl substituted styrenes like alpha-methylstyrene, ethyl-styrene, and the like, the halogen substi- 4 tuted styrenes such as chloroand fluoromonoor di-substituted styrene.

The styrene polymers may contain conventional additives such as dyes or conventional flame retardants such as trisdibromopropyl phosphate, brominated butadiene oligomers such as hexabromocyclododecane, chloroparaffins, if desired mixed with synergists for these flame retardants, such as complex metal compounds or substances which only decompose a high temperatures, for example organic peroxides or hydrocarbons decaying into free radicals such as diamyl. Mineral additives such as talc, phosphates, or organic diluents, as for example citric acid, may also be added.

No particular significance is attached to the manner in which the styrene polymer compositions are ultimately expanded. Thus, it is possible to either physically or chemically accomplish foaming thereof, and if this is to be effected by use of a chemical blowing agent, any of the conventional types can be employed within the context of the invention. These include without limitation the normally liquid, low boiling hydrocarbons such as pentane, and the like, inorganic types such as ferrous oxylate, sodium bicarbonate, ammonium carbonate, a mixture of sodium nitrite and ammonium chloride, etc., and other organic types such as dinitroso-pentamethylene, diazo-amino benzene, p,poxy-bis(benzene sulfonyl hydrazide), alpha-alpha-azobis-(isobutyronitrile), 1 1 -azo-bis-(cyclohexane carbonitrile), benzo-sulfo-hydrazide, urea, bieret, and the like. After incorporation of the blowing agent, the polymeric composition may be cooled to produce an expandable composition or may be immediately expanded, for example, via conventional extrusion or expansion molding techniques or the like.

The following specific examples are included herein to more fully illustrate the present invention, it being understood that they are intended to be merely illustrative and in no way limitative. Average cell sizes disclosed in these examples are determined by (1) cutting several thin slices, conveniently cross sections, at intervals along the extruded foam strip and smearing one side of each slice with ink, (2) mounting each slice on a microscope and measuring the total area of 10 adjoining cells in one place on the slice by the method of least squares, (3) repeating the procedure at four different places on the surface of each slice and using the measurements to calculate the average area of the cells of the slice, and hence their average diameter, and (4) calculating the average value for the cell diameter of the whole strip from the average values calculated for the cells of each slice.

CONTROL EXAMPLE A Into a stirred tank reaction vessel are placed the following materials:

This mixture of ingredients is reacted under suspension polymerization conditions at a temperature of F.

until approximately one hour past the acid test at 125 .rpm. At this point,the following-ingredients are added 'to thepolymerization reactor:

.. The reaction system is then heated up to a temperature of 250C. and the reaction is continued at this temperature for two hours at 150 rpm. After two hours, the reaction mixture is cooled to 1 15F. and there is added thereto 0.024 parts by weight of lime and 7.50 parts by weight of pentane. The reaction system is then heated up to 235F. for V; hour at 150 rpm. After pre-expansion, the expanded polystyrene product is analyzed, and it is found that the average cell size is approximately 140 microns.

EXAMPLE 1 The procedure of Control Example A is repeated except that 0.05 parts by weight of an isobutylene polymer (POLYVIS 200 SH, sold by Cosden Oil & Chemical Company, Big Spring, Texas) having the following properties are added to the initial reaction mixture:

TABLE OF PROPERTIES 1. Molecular Weight (Number Average) 2,700

2. Viscosity Index 121 3. Specific Gravity (60/60F.) 0.909 4. Pounds per Gallon 7.57 5. Flash Point (C.O.C. F) 530 6. Color (Gardner) 1 7. Pour Point (F) +60 After conducting the polymerization and pre-expansion in an identical manner with Control Example A, the expanded polystyrene product is analyzed and found to have an average cell size of about 50 microns.

EXAMPLE 2 The procedure of Control Example A is repeated except that 0.05 parts by weight of an isobutylene polymer (POLYVIS 150 Sl-I, sold by Cosden Oil & Chemical Company, Big Spring, Texas) having the following properties are added to the initial reaction mixture.

TABLE OF PROPERTIES 1. Molecular Weight (Number Average) 2,400

2. Viscosity Index 121 3. Specific Gravity (60/60F.) 0.907 4. Pounds Per Gallon 7.55 5. Flash Point (C.O.C. F.) 5l5 6. Color (Gardner) 1 7. Pour Point (F.) +50 After conducting the polymerization and pre-expansion in an identical manner with Control Example A, the expanded polystyrene product is analyzed and found to have an average cell size of about 60 microns.

EXAMPLE 3 The procedure of Control Example A is repeated except that 0.10 parts by weight of an isobutylene polymer (POLYVIS 30Sl-l), sold by Cosden Oil & Chemical Company, Big Spring, Texas) having the following properties are added to the initial reaction mixture:

TABLE OF PROPERTIES l. Molecular Weight (Number Average) 1,350

2. Viscosity Index 115 3. Specific Gravity (60/60F.) 0.896 4. Pounds Per Gallon 7.46 5. Flash Point (C.O.C. F.) 465 6. Color (Gardner) -l 7. Pour Point (F.) +40 After conducting the polymerization and pre-expansion in an identical manner with Control Example A, the expanded polystyrene product is analyzed and I found to have an average cell size of about 60 microns.

Thus, there is provided in accordance with the present invention an improved expandable styrene polymer composition and an advantageous method for producing expanded styrene polymers by incorporating in the styrene polymer minor amounts of an isobutylene polymer as a nucleating agent.

What is claimed isz 1. A composition suitable for the preparation of an expanded, cellular polymeric product, comprising a styrene polymer, a blowing agent for said styrene polymer and from about 0.02 to 0.15% by weight based upon said styrene polymer of a low molecular weight, liquid isobutylene polymer nucleating agent.

2. The composition as defined by claim 1, wherein said isobutylene polymer has a molecular weight of from about 500 to 5000.

3. The composition as defined in claim 1, wherein said isobutylene polymer is a polymer consisting essentially of polymerized isobutylene monomer.

4. The composition as defined by claim 1, wherein said styrene polymer is homopolystyrene.

5. The composition as defined by claim 1, wherein said isobutylene polymer is present in an amount of from about 0.05 to 0.1% by weight based on said styrene polymer.

6. A method for the production of foamed styrene polymer products, comprising incorporating into a styrene polymer from about 0.02 to 0.15% by weight based on said polymer of a low molecular weight, liquid isobutylene polymer as a nucleating agent and thereafter expanding said styrene polymer by a suitable blowing means.

7. The method according to claim 6, wherein said isobutylene polymer nucleating agent is incorporated into said styrene polymer during polymerization of said styrene.

8. The method according to claim 6, wherein said isobutylene polymer nucleating agent is incorporated into said styrene polymer subsequent to polymerization of said styrene.

9. The method according to claim 6, wherein said styrene polymer is homopolystyrene and said isobutylene polymer is a polymer consisting essentially of polymerized isobutylene monomer.

10. The method according to claim 6, wherein said expansion is accomplished by means of a chemical blowing agent.

11. The composition as defined by claim 1, wherein said blowing agent is an inorganic blowing agent selected from the group consisting of ferrous oxylate, sodium bicarbonate, ammonium carbonate and a mixture of sodium nitrite and ammonium chloride.

12. The composition as defined by claim 1, wherein said blowing agent is an organic blowing agent selected from the group consisting of dinitroso-pentamethylene,

. hydrocarbon. dlaZO-ammo benzene, P5P ysulfonyl 14. The composition as defined by claim 1, wherein 'd b t l l h le 1 ht f hydrazide), alpha-alpha-azo-b1x-(isobutyronitrile), l,lg z 2683?? fig gi m cu ar welg 0 azo-bis-(cyclohexane carbonitrile), benzo-sulfo-hydra- 5 zide, urea and bieret.

13. The composition as defined by claim 1, wherein said blowing agent is a normally liquid, low boiling 

1. A COMPOSITION SUITABLE FOR THE PREPARATION OF AN EXPANDED, CELLULAR POLYMERIC PRODUCT, COMPRISING A STYRENE POLYMER; A BLOWING AGENT FOR SAID STYRENE POLYMER AND FROM ABOUT 0.02 TO 0.15% BY WEIGHT BASED UPON SAID STYRENE POLYMER OF A LOW MOLECULAR WEIGHT, LIQUID ISOBUTYLENE POLYMER NUCLEATING AGENT.
 2. The composition as defined by claim 1, wherein said isobutylene polymer has a molecular weight of from about 500 to
 5000. 3. The composition as defined in claim 1, wherein said isobutylene polymer is a polymer consisting essentially of polymerized isobutylene monomer.
 4. The composition as defined by claim 1, wherein said styrene polymer is homopolystyrene.
 5. The composition as defined by claim 1, wherein said isobutylene polymer is present in an amount of from about 0.05 to 0.1% by weight based on said styrene polymer.
 6. A method for the production of foamed styrene polymer products, comprising incorporating into a styrene polymer from about 0.02 to 0.15% by weight based on said polymer of a low molecular weight, liquid isobutylene polymer as a nucleating agent and thereafter expanding said styrene polymer by a suitable blowing means.
 7. The method according to claim 6, wherein said isobutylene polymer nucleating agent is incorporated into said styrene polymer during polymerization of said styrene.
 8. The method according to claim 6, wherein said isobutylene polymer nucleating agent is incorporated into said styrene polymer subsequent to polymerization of said styrene.
 9. The method according to claim 6, wherein said styrene polymer is homopolystyrene and said isobutylene polymer is a polymer consisting essentially of polymerized isobutylene monomer.
 10. The meThod according to claim 6, wherein said expansion is accomplished by means of a chemical blowing agent.
 11. The composition as defined by claim 1, wherein said blowing agent is an inorganic blowing agent selected from the group consisting of ferrous oxylate, sodium bicarbonate, ammonium carbonate and a mixture of sodium nitrite and ammonium chloride.
 12. The composition as defined by claim 1, wherein said blowing agent is an organic blowing agent selected from the group consisting of dinitroso-pentamethylene, diazo-amino benzene, p, p''-oxy-bis(benzene sulfonyl hydrazide), alpha-alpha-azo-bix-(isobutyronitrile), 1,1-azo-bis-(cyclohexane carbonitrile), benzo-sulfo-hydrazide, urea and bieret.
 13. The composition as defined by claim 1, wherein said blowing agent is a normally liquid, low boiling hydrocarbon.
 14. The composition as defined by claim 1, wherein said isobutylene polymer has a molecular weight of between about 1000 and
 3000. 